Death is an inevitable part of life




Die: loss of individuals, populations (extirpation), or species (extinction)


Is extinction actually a response?


The die ‘response’ is more a a failure to move, adjust or adapt


But patterns of extinction are so important that we need to treat it as a core category

Shaping the tree of life





Modern day biodiversity reflects billions of years of speciation

Is the tree of life being pruned?





Modern day biodiversity reflects billions of years of speciation


Balanced by billions of years of extinction


What is different about today?

Extinction during our time

















2011, cited 3964 times


Never before has an extinction spasm been caused by a single species at such high velocity

Extinction during our time













“The analysis we present here avoids using assumptions … which can suggest very high extinction rates, and which have raised the possibility that scientists are “alarmists” seeking to exaggerate the impact of humans on the biosphere”.

Extinction during our time





















Cumulative percentage of extinct species for vertebrates. Dashed line is number of extinctions expected under a background extinction rate of 2 E/MSY

Extinction during our time





















Number of years it would take for the vertebrate extinctions since 1900 to occur under the background extinction rate of 2 E/MSY

Imperiled amphibians


Current amphibian extinction rates are 100 times higher than historical background rates


  • Caused by:
    • Climate change
    • Habitat alteration
    • Overexploitation
    • Introduced predators and competitors
    • Contaminants
    • Emerging infectious disease

Imperiled amphibians


Current amphibian extinction rates are 100 times higher than historical background rates


  • Caused by:
    • Climate change
    • Habitat alteration
    • Overexploitation
    • Introduced predators and competitors
    • Contaminants
    • Emerging infectious disease


  • What makes an emerging disease emerging?
    • recently discovered
    • recently expanded in geography or host range
    • recently evolved in virulence

Emerging Infectious Diseases


Frog Apocalypse via Batrachochytrium dendrobatidis


Frog Apocalypse via Batrachochytrium dendrobatidis


Imperiled amphibians



Emerging infectious disease


Where did the chytrid fungus come from?


How has it spread?


How does it kill frogs?


Are all chytrid strains equally deadly?


Why are some frog species more susceptible than others?


What can we do to protect amphibian biodiversity?


And on…

Ways of studying population declines



Emerging infectious disease


Where did the chytrid fungus come from?


How has it spread?


How does it kill frogs?


Are all chytrid strains equally deadly?


Why are some frog species more susceptible than others?


What can we do to protect amphibian biodiversity?


And on…

Chytrid story



How does Bd kills frogs











Amphibians are infected with Bd by contact with other animals or by spores floating in the water

Eats away at their skin and triggering fatal heart attacks

Before it dies, a frog may manage to hop its way to a new stream or pond, spreading the fungus further.




Where did Bd come from?


How much genetic diversity does it contain?



Museum specimens point to the oldest known instance from South Africa in the 1930’s.


?Spread around the world in African clawed frogs used for human pregnancy tests?

What makes Bd so deadly?















Genetic evidence of virulence: some of these gene families serve as virulence factors in other fungi that infect vertebrate skin

Differences between the winner and the losers


Why do some frogs NOT die from Bd infection?


















Resistant frogs mount a more robust immune response (via plasticity)

Field studies reveal the heartbreaks?


500 species of amphibians have declined significantly because of the outbreak — including at least 90 species presumed to have gone extinct (2019)

What are the glimmers of hope?


Tracking population recoveries

What are the glimmers of hope?


Direct support to mangers working on-the-ground for amphibian conservation


Pinnacles biologists conducted a study of Bd at Pinnacles National Park from 2006-2007


Tested animals for Bd by swabbing their skin and sending the swabs to a lab for DNA analysis


All three frog and toad species we tested at Pinnacles are infected with Bd


Rarely find dead frogs, and frog populations appear to remain stable

What are the glimmers of hope?


Contributions to conservation more broadly

What are the complexities?


Intentional extinction of pathogens & parasites?

British biotech firm this week got the green light from U.S. regulators to release over 2 million genetically modified mosquitoes in Florida and California


Effort to combat transmission of diseases like Zika, dengue fever and canine heartworm


Genetically modified male (non-biting) mosquitoes mate with invasive female Aedes aegypti mosquitoes, mediating a reduction of the target population as the female offspring of these encounters cannot survive